Grey Alder seeds are relatively easy to germinate and grow. The dormancy within the seed is short and easily broken. This is achieved by a short period of cold stratification in the fridge. You can do this by first soaking the seeds in water for 24 hours. Fully drain away all of the water and place the seeds in a zip-lock freezer bag. Place the seeds in the fridge, it is important that during this period that the seeds do not dry out or are waterlogged otherwise the pre-treatment will be ineffective.

After between 4 and 6 weeks under these conditions the seeds are ready to be sown. In general, many seeds will fail to germinate unless treated in this way, simply sowing untreated seeds in compost at room temperature will not break down the dormancy and germination will be disappointing. You can also choose to mix the seed with moistened vermiculite, fine perlite or sand. These help to stop the seeds from clumping together and allow more between the seeds.

Fill your chosen container with a good quality general potting compost and firm it down well. Suitable containers could be plant pots, seed trays or plug trays or even improvised containers with drainage holes. Firm the compost gently and sow the seeds on the surface, if you have pretreated your seeds without any vermiculite/perlite etc. the seeds will be difficult to separate from each other. If you add a little dry sand at this point and mix thoroughly you will find that the sand separates the seed and makes it much easier to sow. Cover the seeds with a couple of millimeters of vermiculite or failing that a fine layer of sieved compost. Follow with a gentle watering and keep them at room temperature.

Germination will begin from a few weeks following sowing. The seedlings are very small and delicate, they need to be kept out of hot sun until the first true leaves emerge. Shading and a moist seedbed are very important for successful germination. Seedling growth can be very rapid and in their first growing season the seedlings can grow to heights of between 20-50cm. It is preferable to produce shorter, stocky, well branched seedlings rather than long leggy ones. High quality seedlings like these can only be grown if the sowing density is relatively low.

Keep the seedlings well watered and free from competing weeds. Growth will accelerate in the second and subsequent years and the developing young trees should be planted in their permanent position usually by the end of their second year. Large trees of these species do not transplant well and should only be moved during the dormant season.